This invention relates to shearing devices and is particularly directed to a portable power shear for cutting sheet metal and the like. In the past, it has been proposed to provide a power shear head adapted to be mounted upon an electric motor power unit. One such shear is shown in Docken U.S. Pat. No. 2,934,822.
Shears of the general type disclosed in that patent have been manufactured and have proven quite advantageous for cutting light gage sheet metal up to 18 gage. However, it has not been possible to use such shears to cut heavier gage material, such as 14 gage mild steel sheet or 16 gage stainless steel sheet. These heavier gages are commonly used in auto body shops and cabinetry shops fabricating articles, such as kitchen sinks. Consequently, these and other shops working with heavier gage metal have not been able to utilize portable power shears and their significant advantages.
Initial efforts to adapt prior art shears, such as those commercialized under the Docken patent, to cut heavy duty metal failed even when the horsepower of the electric motor drive was increased. One difficulty which was encountered was that the shears produce a tight, small diameter curl of metal which resulted in excessive power requirements. The second difficulty was that the load imposed upon the cam ring employed to oscillate the movable shear blade caused that cam ring to be pulled off the eccentric bushing upon which it was mounted. Thus, the tool had only a very short working life.